The present invention relates to a technique for fastening a magnetic disk to a hub structure by a clamping mechanism. More specifically, the present invention relates to a technique for fastening a magnetic disk to a hub structure by a clamping mechanism, capable of accurately controlling fastening pressure exerted by the clamping mechanism.
In a magnetic disk drive, a magnetic disk, namely, a recording medium, is fastened to a hub, a spindle motor is formed by a coil stator incorporated into the hub and a magnet, and the magnetic disk is driven for rotation by the spindle motor. Generally, the magnetic disk is fastened to the hub by a clamping mechanism. The clamping mechanism fastens the magnetic disk to the hub by pressing the magnetic disk placed on the hub so that the hub is fitted in a circular through hole formed in a central part of the magnetic disk by a thin plate spring, namely, a dished, thin metal plate, and screwing a fastening screw in a threaded hole of the hub so as to apply a proper fastening pressure to the magnetic disk by the thin plate spring.
A clamping mechanism for holding a magnetic disk having a magnetic recording surface and provided with a central hole is illustrated in FIG. 6 of Patent document 1 (Japanese Patent Laid-Open 2004-199760). The magnetic recording surface is provided with a clamping boss to be fitted in the central hole of the magnetic disk, a spring member fixed to the clamping boss to press the magnetic disk against the clamping boss, and a spacing ring placed between the magnetic disk and the spring member. The spacing ring engages loosely with a stepped part formed around the central hole of the magnetic disk.
When the clamping mechanism fastens the magnetic disk to the clamping boss, the fastening pressure exerted by the spring member on the magnetic disk must be properly managed. The magnetic disk will be dislocated when an external shock is given to the magnetic disk drive and servo data cannot be read if the fastening pressure is excessively low. The magnetic disk will be excessively distorted, the surface of the magnetic disk rises and the accuracy of servo control of the tracking operation of a head slider is deteriorated and the head slider collides against the surface of the magnetic disk if the fastening pressure is excessively high. The relation between the deflection of a conical spring employed in such a clamping mechanism and clamping force or fastening pressure is disclosed in Patent document 2 (Japanese Patent Laid-Open 9-265702). Patent document 2 shows that there is a certain relation between the deflection of the conical spring and the fastening pressure.
Generally, a thin plate spring included in a clamping mechanism is provided in its central part with a through hole through which a fastening screw is passed. The thin plate spring is put in place on a magnetic disk mounted on a hub and the fastening screw is screwed through the through hole in a threaded hole formed in a central part of the hub. Then, the thin plate spring is deflected gradually as fastening pressure applied thereto increases. A torque applied to a torque driver to screw the fastening screw in the threaded hole is used for managing the fastening pressure applied by the clamping mechanism to the magnetic disk. Torque necessary for turning the fastening screw increases as an axial force acting on the fastening screw increases due to increase in the deflection of the thin plate spring. Therefore, the conventional magnetic disk drive is able to manage the fastening pressure on the basis of the torque applied to the torque driver.